1. Field of the Invention
This invention relates in general to semiconductor structures, and in particular to hetero-integration of dissimilar semiconductor materials.
2. Description of the Related Art
The material family of GaN (gallium nitride) and related nitride alloys, such as InGaN (indium gallium nitride) and AlGaN (aluminum gallium nitride), has been the subject of intense research. This material family has the promise of being the material of choice for full color displays using LEDs (light emitting diodes) with emission wavelengths covering the entire visible light spectrum, for high density data storage using violet laser diodes, and for high power electronic applications.
The anticipated market size for these lines of products is tremendous. For example, all DVD (digital video disks) manufactured from year 2001 onward will use nitride violet laser diodes.
All the structures demonstrated to date have been fabricated in thin film nitride epitaxially grown on either Al2O3 (sapphire) or SiC (silicon carbide) substrates. One of the major challenges in nitride technology development is epitaxial material quality. Typical dislocation density is between 108-1010 cmxe2x88x922. Threading segments of the dislocations extend in the direction perpendicular to the film surface, and thread through the entire epitaxial film thickness. It has been proven that high dislocation density limits the lifetime of laser devices and carrier mobility in electronic applications.
A variety of approaches have been used to reduce dislocation density. Two of the most successful ones are known as LEO (lateral epitaxial overgrowth) and PE (pendeo-epitaxy). LEO consists of patterning the substrate surface with a SiO2 (silicon oxide) mask, and growing nitride films upward and then sideward from the open areas in the mask. Since dislocations in this crystal structure only thread upwards, the lateral overgrowth portion of the nitride film can be made relatively free of dislocations.
PE represents an improvement over LEO. PE consists of first growing a film of highly dislocated nitride film directly on top of the substrate. This is followed by a patterning step using a mask layer such as SiO2. The nitride film under the open areas in the mask is etched away, and another mask layer is deposited on the bottom of the etched area to prevent nitride nucleation. Finally, a lateral regrowth of nitride film takes place. The film growth follows the direction of lateral, up, and lateral.
PE requires at least one nitride regrowth step, but offers more useable area for device fabrication. This is because PE eliminates the high dislocation density region above the mask openings as in LEO.
Thus, there is a need in the art for a simplified approach to reducing dislocation density in epitaxial films. More specifically, there is a need in the art for a simplified approach that can be used in mass production of devices.
To minimize the limitations in the prior art described above, and to minimize other limitations that will become apparent upon reading and understanding the present specification, the present invention discloses a method, structure and article of manufacture related to hetero-integration of dissimilar semiconductor materials. A mask is created on a semiconductor substrate, wherein the mask includes one or more openings, and each of the openings includes one or more overhangs. The overhangs cover a hetero-epitaxial interface region between a film expitaxially grown on the substrate and the substrate itself, thereby preventing a xe2x80x9cline-of-sightxe2x80x9d view along a surface norm of the substrate in the hetero-epitaxial interface region between the epitaxial film and the substrate. There is only one hetero-epitaxial interface region for each of the openings, which results in only one epitaxial growth front coalescence per opening, thereby reducing the number of highly defective regions from epitaxial growth front coalescence by a factor of two.